class ListNode {
    private ListNode next;
    private ListNode prev;
    private int val ;
    public ListNode(int val )
    {
        this.val = val;
    }
}
class List{
    private ListNode head;
    public List(ListNode node)
    {
        if(head == null)
            head = node;

        while(head!=null)
        {
            head = node.prev;
        }
    }
}
class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {

    }
}
public class test1 {
    public static void main(String[] args) {
        ListNode l1 = new ListNode(1);
        ListNode l2 = new ListNode(2);
        ListNode l3 = new ListNode(4);
        ListNode l4 = new ListNode(1);
        ListNode l5 = new ListNode(5);
        ListNode l6 = new ListNode(6);


    }
}
